Centrifugal pumps and compressors



Feb. 11, 1958 E. B. DOVE CENTRIFUGAL PUMPS AND COMPRESSORS Filed June 1, 1954 FIG.

FIG. 3;

' Inventor M6, 9 g,

By warm,

Attorneys United States Patent CENTRIFUGAL PUMPS AND COMPRESSORS Ernest Baker Dove, Luton, England, assignor to D.

Napier & Son Limited, London, England, a company of Great Britain Application June 1, 1954, Serial No. 433,783 Claims priority, application Great Britain June 1, 1953 2 Claims. (Cl. 103-103) This invention relates to fluid compressors, or pumps, of the centrifugal type and is particularly though not exclusively concerned with compressors or pumps intended to be operated at high speeds.

The impellers of such centrifugal compressors or pumps require to be accurately located in the axial direction in order to avoid the blades of the impeller fouling the walls of the casing. This axial location normally requires accurate manufacture and skilled assembly, necessitating in some cases the use of special shim washers, and moreover may be upset by thermal expansion of the parts.

It is an object of the invention to provide an improved compressor or pump of the kind referred to which will be simple and economical to manufacture, simple to assemble and will obviate or reduce these disadvantages.

According to the present invention a fluid compressor or pump comprises a casing within which a rotary centrifugal impeller is mounted for rotation in such manner as to permit at least limited free movement thereof in at least one axial direction, at least part of one of the radial edges of the impeller blades being so inclined rearwardly to the direction of movement of the blades that the action of the fluid between such edge and the adjacent wall of the casing when the edge of the blade approaches the wall, tends to urge the impeller bodily in the opposite axial direction.

According to another aspect of the invention, a fluid compressor or pump comprises a casing and a rotary centrifugal impeller mounted within the casing and arranged to have at least limited free movement in both axial directions, at least part of both opposite radial edges of one or more of the impeller blades being so inclined rearwardly to the direction of movement of the blades that the action of the fluid between any such edge and the adjacent wall of the casing when the edge of the blade approaches the adjacent wall of the casing, tends to urge the impeller bodily in the opposite direction.

The impeller therefore may be of the single entry type and may include a thrust bearing or the equivalent to locate the impeller in one axial direction while the formation of the edges of the blades acts to urge the impeller against such a thrust bearing. In a preferred construction, however, the impeller is of the double-entry type and is fully floating in both axial directions.

The invention may be performed in various different ways, but one specific embodiment as applied to a high speed liquid pump designed for use in conjunction with a rocket motor in a guided missile, will now be described by way of example with reference to the accompanying drawings, in which:

2,822,758 Patented Feb. 11, 1958 Figure 1 is a fra mentary sectional view through 'the axis of the pump,

Figure 2 is an end view of the impeller of the pump, and

Figure 3 is an enlarged diagrammatic developed view of a section through a blade of the impeller and the adjacent walls of the pump housing in a plane normal to a radius through the blade. The figure also shows diagrammatically the approximate fluid flow distribution in the neighbourhood of the blade.

Such pumps may be required to run at high rotational speeds, for example 20,000 to 35,000 R. P. M., since the space requirements are severely limited. On the other hand the life requirements of such a pump are relatively short, and it is desirable that the pump should be capable of being assembled by unskilled labour.

In this example the pump impeller is of the doubleentry type and comprises four radial plate-like blades 1 secured to a central hub 2, the profile of the blades in cross-sections containing the axis of the impeller (as shown in Figure 1), being tapered somewhat from a maximum width adjacent to the hub to a minimum width adjacent to the tips of the blades. The blades are arranged to lie in planes containing the axis of the impeller, and are of the non-twisted type.

The pump casing 3- is of slightly larger dimensions than the impeller both in the axial and radial direction, the axial clearance being determined by manufacturing tolerances and by the efliciency requirements of the impeller.

The hub 2 of the impeller is internally splined and is mounted on a driving shaft 4 provided with cooperating splines, so as to be free to move in an axial direction, while being accurately located for radial or rotational movement. The splines are conveniently formed by a broaching process which enables the impeller to be accurately mounted on the shaft by unskilled labour.

The opposite radial edges 5 and 6 of each of the blades are chamfered off, preferably by a simple grinding operation, to form surfaces which are inclined rearwardly at an angle of 5 to the direction of motion of each blade.

When the impeller is centrally positioned in an axial direction within the pump casing the velocity distribution of the pumped fluid (as shown diagrammatically in the lower part of Figure 3) is substantially symmetrical about the central plane of the casing and two equal and opposite axial force components are produced on the inclined edge surfaces 5 and 6 of the blades. When the impeller moves axially away from the central position, however, the velocity distribution is disturbed, the velocity being increased at one blade edge and decreased at the opposite edge. The two force components are no longer equal and the resultant total axial force tends to move the impeller bodily on the splined driving shaft to restore it to its central position.

Thus the invention provides an eflicient high speed pump, which can be assembled without accurate axial location of the impeller.

What I claim as my invention and desire to secure by Letters Patent is:

1. A centrifugal pump comprising a casing having oppositely disposed axially spaced end walls and a rotary double entry centrifugal impeller having blades provided with opposite radial edges conforming to the adjacent surfaces of the end walls, means mounting said impeller for rotation within the casing and for limited free movement in both axial directions up to the point where the opposite radial edges of the impeller blades contact their respective adjacent end wall of the casing, at least part of both opposite radial edges of the impeller blades at locations axially opposed to the axial end walls of the casing being inclined rearwardly to the direction of movement of the blades relative to the casing whereby the action of the fluid between such blade edge and the adjacent wall of the casing, when the edge approaches the wall, tends to urge the impeller bodily in the opposite axial direction.

References Cited in the file of this patent UNITED STATES PATENTS 1,183,075 Kiefer May 16, 1916 1,595,636 Walters et al Aug. 10, 1926 2,332,411 Swanson et a1 Oct. 19, 1943 

